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1965 merc 50 hp no spark

T

Timbogarb

Member
I've been working on getting a merc 500 going after buying it from a friend. Hasn't run in 10 years so first thin I did was checked the gear oil in the Lower unit, change the impeller clean carbs etc. But no spark. Replaced condencer and cleaned points. Nothing. Any ideas?
 
Hi, Timbo, did you disassemble the points and clean to bare metal? Afterwards it's a good idea to polish with some crocus cloth then degrease the points and set the gap to approx .010"

I always bench-test the mag before installing. You can hold a screwdriver shaft against the metal case of the mag, with the tip approx 3/8"-1/2" from the flat copper contact. Give the mag drive shaft a stout spin (clockwise as viewed from the top), and spark should easily jump a 3/8" or more gap.

You may need to pull the mag again to do this check. It's possible to have a bad rotor and then spark will be shorted to the mag shaft and won't get out of the distributor.

Other possibilities are a bad coil, you can do a resistance-check and can also remove the coil to check for physical damage (cracks and arc marks). The allen screws on the end of the mag casing hold the coil in; if these screws are still lockwired, cut the wire and loosen those screws to remove the coil.

Last thought is the terminal at the side of the mag housing. The "kill" wire is connected to this terminal and when the key is turned to the "OFF" position, the mag is shorted to ground. There may also be a switch full of mercury (i.e. "mercury switch") connected to the "mag short" terminal. Sometimes these go bad, so disconnect all wires at the terminal and then see if you have spark.

The screw that goes thru the casing is kept from shorting out against the casing via a bakelite insulator, if this is assembled improperly or broken, the screw could be grounded, thus killing spark.

Anyway, there's a few things to look at. The Mercury magneto is a pretty reliable unit but can have issues, as will any 50-year-old mechanical device.

Let us know what you find and if you post a serial # we can guide you to the correct parts for your motor........ed
 
Thanks for that extensive reply. I do have a specific question about the coil. I'm getting only .03 on the meter for resistance. Seems a little low. Will be back at the cottage on Sat and will bench test and check all of your suggestions. Will post any results
 
The primary side of the coil will be a fairly low resistance, whereas the secondary side will be much higher. Let us know what you find.......ed
 
Well, got spark on all cylinders and occasional ignition(fire puff bang) on occasion so I'm going to clean the carbs tomorrow. I'm concerned about the timing although the line on the fly wheel and the magnito arrow are lined up. Hopefully just a dirty carb. Any suggestions ?
 
Timbogarb said:
Well, got spark on all cylinders and occasional ignition(fire puff bang) on occasion so I'm going to clean the carbs tomorrow. I'm concerned about the timing although the line on the fly wheel and the magnito arrow are lined up. Hopefully just a dirty carb. Any suggestions ?
Click to expand...

Carbs can definitely be a maintenance item. You can pull the brass main jet plug at the front bottom of each carb; pull the idle mixture needle; and pull the float bowl top, all without removing the carbs. This gives you quick access to the most problematic areas.

Blow out with carb cleaner followed by compressed air if you've got it. Check the floats, if they're deteriorated replace with the newer ethanol-resistant type, still available. Check float needle height & drop, float spring height, adjust if necessary.

Note that if you find a bunch of nasty deposits when you start taking the carbs apart, they need to come off for a thorough cleaning.

Carb packing kits are available for minor servicing/cleaning and should be all you need except for extreme cases. A lot cheaper, too.

You may find the fuel pump diaphragms old & deteriorated, the diaphragm/gasket kits are still available and not too $pendy.

Some very useful info at this site: http://www.maxrules.com/carbindex.html
 
Thanks ed. I realized why I was getting the bangs. When I disconnected the mag/distributor I left a short piece of the ignition kill switch with the unit. When I reinstalled it I forgot to put some electRica tape on it and the bare wire was touchinges the housing. So with the vibration of the starter, a spark would get through, igniting all the vapour. Didn't clean the carbs because once I got it started it held the smoothest idle I've seen on a 2 stroke. Put a hole tank of fuel through it and ran like new. I do think I can get more out of it with some adjustments to trim (fixtures pin type) and leaning the mix a little. Maby a more aggressive prop. Seems to not be working hard when at full throttle that's why I think it's the prop. Thanks again for the advice.
 
Sounds like you've got a good one! These 44-c.i. inline fours were some of the best motors Merc ever built.

Definitely get 'er propped to the correct rpm range and she'll run a lot better. Somewhere between 5300-5500 is good for WOT with a light load (driver only).

Have Fun!.........ed
 
I've been watching videos on this motor and am now seeing that I'm not getting the rpm or fast response. Couldn't get it up on plain with 2 adults and a dog. Only got it on a 16 foot fiberglass
 
Well, it's just a 50hp after all! A really good indicator of a too-tall prop is if you can get it to plane with just you in the boat.

Maybe a prop with 2"-less pitch would work, but it'd be better if you knew WOT rpm 'cause then you could make a more accurate "guesstimate" on which size of prop would work best.

Can you tell what's the pitch of the existing prop? Many times the prop part # is stamped into the body of the propeller.
 
Timbogarb said:
I'll have to answer that on Sunday. I was wondering if the spark advance may be an issue. Like I said, 2 people and Maby only 7 mph
Click to expand...

Unless you have reason to think the spark advance stop was messed-with, it may never have been changed from its original setting.

If you've confirmed that belt timing is OK (and since you said it idles well, it can't be too far off), I'd check to make sure the distributor rotates fully to hit the spark stop, and at full throttle both carb butterflies are wide-open.
 
Hey ed, may be a dumb question, but do you know if this motor has a tell tale/pisser? The engine runs cool and water comes out of the upper exhaust port and through the prop whth the majority of the exhaust. I can't seem to find a hole for a tell tale, or any mention of one in any manuals.
 
The 1965 model should have a hose coming off the bottom of the exhaust manifold cover (Port side), crossing over at the back of the motor (lower cowling aka 'motor pan'), and exiting at the rear Stbd side of the lower cowling. Sometimes these are plugged with silt/debris/bugs and a blast of compressed air up the telltale hole can help clear the obstruction.

On old motors, sometimes the passage within the manifold cover is plugged with salt/silt deposits and it'll never pass water without removing the cover and cleaning.

In that case, you should find a 1/8"-NPT slotted plug at the top-rear of the block, this goes into the main coolant passage cavity of the block (behind the water jacket cover on the back of the block), and you can install a fitting up there, as an alternate feed for the telltale.

A lot less work than pulling the exhaust manifold cover, and actually a better place for a telltale, since it's the high-point of the block and any air entrapped at the top will be bled off.

Hopefully a good shot of air will fix 'er up.

HTH.........ed
 
Yup, I'm going to install that line in the top. Still not sue what's going on with the power. When punching it from a stand still it launches the boat like you would expect, but as I start moving faster, it seems to not have any interesa in going faster. Dogs when turning at speed, won't get up on plane with two people. Can't get more than 15mph empty boat 1 person. Put sea foam through it and now am seeing oil in the water and cloudy white water coming from exhaust when idling. Think it's an oil water sign. Checked oil in lower unit and still clean (no water). Is this an indication of running too Ritch. Like I said, it's a 16 foot fiberglass 1 driver, my neighbor has an 18 foot pontoon and gets 25mph with 4 people with a 50h. Thanks
 
I don't have a manual, I need to pick up a timing gauge. Dose that explanation the oil in the water? Is this an indication of the motor running to rich? I'm not at the cottage until the weekend so I can't do much now. It's funny how strong it is when opening it up from a stop then just seems to loose interest as it speeds up
 
It runs smoothly, and I'm still getting the un burned fuel and lack of power at wot might be time to take it in. Can't find the tools to do the timing and have leaned the idle but still getting the fuel and oil in the exhaust
 
How big is the boat you have it on? I doubt you will find a mechanic that will work on it. The only special tools you may need is a dial indicator and a multimeter. Are the carbs opening up exactly the same time? Basically you need to adjust the Max timing advance and the throttle pickup. Have you done a cylinder drop test? While idleing pull a plug wire and then put it back on the engine should respond the same on all four cylinders. Use a good pair of insulated pliers it bites. Its not that hard once you figure it out. Put the dial indicator in the #1 plug hole and find the top of the piston stroke and zero the dial indicator the rotate the flywheel clockwise to where the dial indicator reads .235 inches before TDC. Then connect your multimeter to the magneto frame and the ground post on the magneto and turn the magneto until the points just open. Then adjust the max spark advance set screw to barely touching the stop on the distributor. That is max spark advance make sure the throttle lever is not binding between the carb and the pickup plate you should be able to slide a .015 feeler guage between the two. If binding it will wear out the shaft in the upper carb. Then turn the flywheel clockwise slowly to .015 Before TDC retard the timing and thenadvance it until the points just open. That is when the carbs should just begin to open, agjust the pickup plate to barely touching the throttle lever on the carbs. Make a couple marks on the flywheel for future reference using a good point on the powerhead. You can actually reference those marks with a timing light for future diagnostics. They did not use degrees back then they used the height of the piston in the stroke.
http://www.ebay.com/itm/Vintage-Fed...019988?hash=item4d4bab9d94:g:EoQAAOSwCGVX3wCA
What I did working on old 9.8 mercs was busted out the center of a spark plug and stuck the dial indicator in with a few o-rings to hold it tight. Find the top of the stroke and then zero the dial and rotate the flywheel to desired setting and just zero the dial. Never turn the flywheel counterclockwise it will mess with the impeller just rotate clockwise until you get to zero on the guage and mark a locator on the flywheel. You can use a calipers if your creative. If you didnt mess with the max spark advance it should be good but every time you pull the carbs you need to check adjust the throttle pickup.
 
I'll try next weekend. It's a 16 foot fiberglass. I'm lucky that the merc dealership in bancroft that knows my motor inside and out. I just need to pick up a dial indicator. Thanks
 
That should bring the boat up on a plane rather quick unless the double bottom is full of water. Did you try different trim angles on your sea trials?
 
The boat had a double bottom, I've cut it all out due to rot and water. Boat bottom is gutted. I've trimmed up so that it will get on plain just with myself. Maby gets me up to 18 mph on smooth water. My son's 5 horse can dust me if I have 2 people and him in his aluminum.seems like I'm only getting 15hp out of it. Lower rpm seems to have more power . I have the Cowell off and can see both throttle opening fully. Uses fuel excessively and lots of oil in the water while running
 
Either bad fuel pump diaphragms causing excess fuel to be sucked into the engine, or one or 2 of the cylinders isn't hitting and the unburnt fuel is just dumping out the exhaust.

Post a video of the motor running in the lake, since there are many experienced ears here, just listening to the motor run will tell us a lot.
 
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